The invention relates to an apparatus for piecing-up a wrap yarn being produced with a hollow spindle carrying a bobbin with a wrapping thread and arranged between a pair of delivery rolls and a pair of takeoff rolls. A housing concentrically surrounds the bobbin with its wall having openings for the passage of air. A suction duct is arranged between the pair of delivery rolls and the hollow spindle.
For piecing-up, it is known in an apparatus of the above-mentioned kind to deflect a spinning fiber bundle emerging from the pair of delivery rolls by means of a suction air stream produced by a suction apparatus into the suction duct where it is entrained by the suction air after the hollow spindle is stopped. The fiber bundle is united with the wrapping thread delivered back through the hollow spindle with the wrapping thread, and twisted with these by starting the hollow spindle (DE-OS No. 2,753,349). The openings in the jacket of the housing surrounding the bobbin through which air can flow enables an air vortex to be produced within the housing which automatically results in the exposing of a broken wrapping thread on the spindle.
It has been found to be disadvantageous in the known piecing-up process that because of the air passage openings in the housing a suction apparatus with a high suction power is required in order to produce in the hollow spindle a strong enough suction to deliver the wrapping thread back into the suction duct. The efficiency of the piecing-up process is thereby reduced. This is even more the case if, on technological grounds for the spinning operation, further openings are provided in the housing. A further disadvantage consists in that because of the relatively large cross section of the suction duct for the required suction effect, the guiding of the spinning fiber bundle, together with the wrap yarn and the wrapping thread, is not always ensured.